Re: [TCML] The truth about LTR, STR, and resonant modes

[Mddeming@xxxxxxx]

Hi John,
 
Exceptional clarity and conciseness. You definitely learned your writing  
skills in the era before text-messaging. ;^)
 
Matt D.
 
In a message dated 5/28/08 2:21:00 A.M. Eastern Daylight Time,  
FutureT@xxxxxxx writes:

In a  message dated 5/27/08 6:21:03 PM Eastern Daylight Time, FutureT@xxxxxxx 
 
writes:

> >If a pig or PT coil is run with a   small
> >cap at high bps, then the ballast L has to be reduced to  let  in
> >more power (if long sparks are desired).  Then  the coil is  truly
> >running in STR mode.
> 
>  >John
> 

Correcting my post above here.  Such a coil as  above
(small cap, high bps), is not necessarily STR mode.
This can be  resonant or LTR mode also.  It all depends on
the ballast setting  (explained below).  My other recent posts 
mostly spoke of 120 bps  operation but the comments
in those posts
apply to higher bps operation  also, except the power
factor might not be as good at the higher  bps.

Deano is most likely correct that most folks are
probably  running in resonant mode with their pig and
PT systems.  Resonant mode  is not solely dependent
on the cap value for a given non-shunted  transformer.
Any cap value can be run in LTR, STR, or resonant
mode by  adjusting the ballast as needed to give the
respective mode.  This is  mostly independent of
the transformer size (within reason of course).   A
too large cap will not be able to be charged to
a reasonable voltage,  etc.  

NST's (and OBITS), i.e. shunted, transformers are  a
special case.  For a given NST, a given cap value is
either LTR,  STR, or resonant.  This is not true for
unshunted transformers such as  pigs and PT's.  These
transformers are always run with a  ballast.  The
setting of the ballast will determine, along with the  
cap value, whether the system is running in LTR,
STR, or resonant  mode.  The transformer doesn't
really enter into the equation except  for impedance
transformation which determines how much ballast
L is  needed for a particular mode, and also the
transformer must be able to  handle the power, etc. 

It's not correct to say, "this pig has an  LTR
value cap" or something similar.  The cap itself
doesn't  determine if the system is running in LTR
mode.  This will  be  determined by the setting of
the ballast also.  Of course the spark  length has to
be considered.  Longest sparks may be produced
in  resonant mode, or slightly LTR.  In resonant
mode, the reactance of  the ballast "cancels" the
reactance of the cap, and this lets the  maximum
power enter the system.  This should give  longest
sparks.  LTR may work somewhat similarly up to
a  point.  There are issues such as inductive kick
to consider.  As  the ballast is increased in 
inductance, this will create an LTR mode in  
high bps systems, but it will also tend to 
throttle back the power and  reduce the spark
lengths.  

Coilers should select their cap  value based on
the needed spark length, and the capabilities of
the  transformer.  If the transformer is extra powerful,
they can select a  smaller cap, and adjust the
ballast for resonance or LTR and still get  rather
short sparks if that's what they want.  If they
want longer  sparks, then just use a larger cap,
and again adjust for resonance or  slight LTR.  If one wants
super long sparks, then use an even  larger
capacitor and again adjust for resonance or
slight LTR.   This may force the pig to provide
double its rated power, but pigs can  handle that.

Folks used to talk a lot about each coil having
its own  personality so to speak.  I believe one
cause of that was the relative  cap value versus
the transformer power versus the ballast  setting,
thereby making the coil run either LTR, STR, or
resonant.   I used to often talk about how 
important it is to use the proper value cap  for
120 bps coils, but the proper value cap is
important for high bps  coils too, so that the 
spark lengths will be correct, when the  ballast
is set (tuned) correctly.  This is what Bill Wysock
talks  about when he talks about tuning the ballast.
This is probably creating a  resonant or slight LTR
condition for maximum efficiency and best  power
factor.  I'm not sure exactly what adjustment
(LTR, STR, or  resonant) will give best power factor
with high bps, but surely one of them  will be best
in that regard.  

In some cases folks may use a  capacitor that
is larger than optimal for the desired spark length.
This  may make it necessary to misadjust the
ballast and introduce inefficiency  or a bad power
factor into the system to deliberately reduce the 
spark  length.

Some may say that fixed LTR, STR, and resonant
cap values  are valid for pigs and PT's.  This
may be true if the transformer is  run at its
rated power.  But if it's not run at it's rated  power,
if it's run at either higher or lower power, then
the LTR, STR,  and resonant values change.
This is why it's best to look at it from  both
and cap value *and* ballast inductance value
perspective.   Otherwise the situation can be very
misleading.  

I hope the  above is written clearly enough.
I kind of jumped around with the  thoughts.  

John








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